An Interesting Two Wheel Ask MetaFilter Question

realpseudonym asks: Is it safer to do a 5 mile commute on city streets on a bicycle or a motorcycle? on Ask MetaFilter.

Let's say we have a 5 mile commute along fairly busy 4 lane city streets. Cars are parked on the curbs on both sides of the streets. Some of the streets are very commercial with cars coming in and out of driveways. There are city buses.

Assume that I am a perfect driver, and that accidents only happen because somebody doesn't see me or sees me and misjudges how close they are to me.

Am I safer riding a motorcycle with full safety gear (going up to 35 mph) or riding a bicycle with only a bicycle helmet (up to 15 mph)?

My first thought was that the bicycle is obviously safer because of the lower speeds involved. On the other hand, I thought the motorcycle might be safer because you move at the same speed as traffic; whereas on the bike, angry drivers will constantly be trying to pass you.

All other things being equal, it is an interesting question and one that I don't think has a perfect answer.

I'm both a biker and a cyclist. I ride a streetbike and an off-road bicycle primarily. Yes, I do ride my bicycle on the street but not as a general rule. I either ride to a trail or am crossing a road to get back onto a trail.

My quick response to this is the motorcycle because I have far more control over a less controllable environment on my motorcycle on the street than I do with my bicycle. In the woods, I have yet to see a tree jump into my path. I have yet to have a branch suddenly appear and knock me off my bike.

I think a motorcycle is probably going to be safer on the commute. Now keep in mind that this question doesn't ask about total cost of ownership or anything but the factor of safety in doing one or the other over the same stretch of road.

If the question were framed differently, say that the commute was the same length but the bicycle was able to make the journey through a park system without other vehicles then the bike wins hands down since it is far harder to get run over when there aren't any cars around.

I'm interested in what other cyclists might think about this question given the framing. Please reply in the comments.